Matter of our surrounding |part 2 9th cbse Can Matter change its state? Effect of change of temperature Effects of change of pressure Evaporation Factors affecting evaporation How does evaporation cause cooling Summary Matter of our surrounding |part 2

2. CONTENTSC
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1.4 Can Matter Change its
State?
1.4.1 EFFECT OF CHANGE OF
TEMPERATURE
1.4.2 EFFECT OF CHANGE OF
PRESSURE
1.5 Evaporation
5
1.5.1 FACTORS AFFECTING
EVAPORATION
6 1.5.2 HOW DOES EVAPORATION
CAUSE
COOLING?

3. 01 1.4 Can Matter Change its
State?

4. We all know from our
observation that water
can exist in three states of
matter–
• solid, as ice,
• liquid, as the familiar water,
and
• gas, as water vapour.

5. 02 1.4.1 EFFECT OF CHANGE OF
TEMPERATURE

7. On increasing the temperature of solids, the
kinetic energy of the particles increases.
Due to the increase in kinetic energy, the
particles start vibrating with greater speed.
The energy supplied by heat overcomes the
forces of attraction between the particles.

8. The particles leave their fixed positions and
start moving more freely.
A stage is reached when the solid melts and
is converted to a liquid.

9. What is Melting point?
The temperature at which a solid
melts to become a liquid at the
atmospheric pressure is called its
melting point.

10. The melting point of ice is 273.16 K*. The
process of melting, that is, change of solid
state into liquid state is also known as
fusion.

11. When a solid melts, its temperature
remains the same, so where does the
heat
energy go?
You must have observed, during the
experiment of melting, that the
temperature
of the system does not change after the
melting point is reached, till all the ice
melts.

12. This happens even though we continue to
heat the beaker, that is, we continue to supply
heat. This heat gets used up in changing the
state by overcoming the forces of attraction
between the particles. As this heat energy is
absorbed by ice without showing any rise in
temperature, it is considered that it gets
hidden into the contents of the beaker and is
known as the latent heat. The word latent
means hidden

13. The amount of heat energy
that is required to change 1 kg of a solid into
liquid at atmospheric pressure at its melting
point is known as the latent heat of fusion.
So, particles in water at 00 C (273 K) have
more energy as compared to particles in ice
at the same temperature.
When we supply heat energy to water,
particles start moving even faster.

14. Particles from the bulk of the
liquid gain enough energy to change into the
vapour state.
The temperature at which a liquid
starts boiling at the atmospheric pressure is
known as its boiling point.
For water this temperature is 373 K
(100 0C = 273 + 100 = 373 K).

16. Fig. 1.7: Sublimation of ammonium chloride

17. A change of state directly from solid
to
gas without changing into liquid
state (or vice
versa) is called sublimation.

18. 03 1.4.2 EFFECT OF CHANGE OF
PRESSURE

19. Fig. 1.8: By applying pressure, particles of
matter can
be brought close together

21. 04
1.5 Evaporation

22. Do we always need to heat or change
pressure
for changing the state of matter?
We know that particles of matter are
always moving and are never at rest. At a
given temperature in any gas, liquid or solid,
there are particles with different amounts of
kinetic energy.

23. 05
1.5.1 FACTORS AFFECTING
EVAPORATION

24. You must have observed that the rate of
evaporation increases with–
• an increase of surface area
• an increase of temperature
• a decrease in humidity
• an increase in wind speed

25. 06
1.5.2 HOW DOES EVAPORATION
CAUSE
COOLING?

26. In an open vessel, the liquid keeps on
evaporating.
The particles of liquid absorb
energy from the surrounding to regain the
energy lost during evaporation.
This
absorption of energy from the surroundings
make the surroundings cold.

27. S u m m a r y
Matter is made up of small particles.
• The matter around us exists in three states— solid, liquid
and gas.
• The forces of attraction between the particles are maximum
in
solids, intermediate in liquids and minimum in gases.
• The spaces in between the constituent particles and kinetic
energy of the particles are minimum in the case of solids,
intermediate in liquids and maximum in gases.

28. • The arrangement of particles is most ordered in the case of
solids, in the case of liquids layers of particles can slip and
slide over each other while for gases, there is no order,
particles
just move about randomly.
• The states of matter are inter-convertible. The state of matter
can be changed by changing temperature or pressure.
• Sublimation is the change of gaseous state directly to solid
state without going through liquid state, and vice versa.
• Boiling is a bulk phenomenon. Particles from the bulk (whole)
of the liquid change into vapour state.

29. • Evaporation is a surface phenomenon. Particles from the
surface gain enough energy to overcome the forces of attraction
present in the liquid and change into the vapour state.
• The rate of evaporation depends upon the surface area exposed
to the atmosphere, the temperature, the humidity and the
wind speed.
• Evaporation causes cooling.
• Latent heat of vaporisation is the heat energy required to change
1 kg of a liquid to gas at atmospheric pressure at its boiling
point.
• Latent heat of fusion is the amount of heat energy required to
change 1 kg of solid into liquid at its melting point

30. THANK YOU